Diets all share the same principle: eat less energy than you need. This results in weight loss. However, the weight loss is usually a combination of a loss of body fat and muscle mass. Additionally, one's bones may begin to weaken, albeit very slowly, while on a diet, which could have serious long-term consequences. Thus, the investigators believe that the goal of any weight loss strategy should be to lose body fat and spare muscle. The investigators reasoning is two-fold. 1) Fat is not only stored under the skin, but also in and around the internal organs. When this occurs, the organ itself may not function properly. Losing fat mass is a very good thing from a health standpoint, since fat is not just a storage site for extra energy. Scientists have now shown that 'extra' body fat itself can actually secrete substances and when these substances get into your blood, they cause many problems and may even contribute to the development of diabetes. 2) Sparing muscle as an individual loses weight is very important. Muscle is a very 'metabolically active' tissue and is, by analogy, like the body's furnace. Muscle burns fuel from the food individuals eat and also from stored fuels, like fat. Hence, it's easy to see why you don't want to lose muscle because you'd be losing one of your body's best fat burners. More importantly, muscle is also a big storage site and furnace for blood sugar. In people with diabetes (elevated blood sugar), a big part of the problem is with their muscles - they simply do not take up and store or burn enough sugar. For these reasons, your goal should be to lose fat and preserve muscle while dieting.

There are many different diets to choose from (e.g. high protein, low carbohydrate, high fat, high fiber, etc.). A diet that has been shown to be quite successful, however, is one that is higher in protein (but not excessive). Thus, in this study, the investigators are proposing to test whether a higher protein (with dairy) and calcium diet promotes body fat loss and muscle mass retention. The investigators believe that a diet higher in protein (with an emphasis on dairy), but still within accepted healthy ranges, with higher dietary calcium may result in greater loss of body fat and retention of muscle than a diet with a conventional amount of protein and adequate calcium or a conventional amount of protein with little calcium (i.e. low dairy). Based on previous research, the investigators think that people with low calcium intakes to begin with would stand to benefit the most. There is also a good reason to think that the high protein/high calcium diet may result in greater reductions in blood cholesterol and blood sugar, both of which would reduce a person's risk for heart disease and diabetes.

The investigators will test this diet in premenopausal women who are overweight or obese. The investigators believe that this group is a good one to target for several reasons. First, women of this age who are overweight or obese are, if they continue to carry this excess weight, are at serious risk for developing chronic diseases such as heart disease, diabetes, and possibly cancer at an early age. Second, these women will often begin to gradually consume less dairy because many perceive dairy foods as fattening. Thus, if the investigators proposals are correct the investigators will hopefully be able to equip health professionals with a tried and tested, palatable, dietary strategy in a population segment who, because of their age, would benefit greatly were their disease risk to be reduced.

Subjects will perform exercise (aerobic and resistance) 7d/wk and will exercise supervised 5d/wk. Exercise will be carried out to expend 250 kcals/day. Supervised resistance training sessions will take place 2 days/wk and aerobic exercise will take place every day. During the resistance exercise sessions, subjects will engage in a circuit weightlifting routine using guided motion machines. During the aerobic sessions, subjects may choose whatever exercise modality they like (e.g. walking on track or treadmill, biking, elliptical, etc.). Subjects will wear devices that measure energy expenditure to get a better idea of the intensity and duration needed to expend 250 kcals with their exercise machine/modality of choice.

Behavioral: Dietary - Caloric Restriction

Subjects will be counselled on their respective hypocaloric diets during the 16 wk period. Adherence to the prescribed diet will be assessed via collection of assigned food records (biweekly), frequent contact with subjects, and regular dietary counseling sessions. The daily dietary energy deficit will be 500 kcal per day based on the subjects' estimated daily caloric requirements (based on height, weight, age, sex), multiplied by a sedentary activity factor.

Additionally, subjects will consume 2 drinks per day that will differ depending on their randomization allocation. Subjects in the Dairy Protein and High Dairy Protein group will be provided with dairy products (e.g. milk, cheese, yogurt) to consume on a weekly basis to help facilitate their prescribed dairy and dietary protein intake.

Subjects will perform exercise (aerobic and resistance) 7d/wk and will exercise supervised 5d/wk. Exercise will be carried out to expend 250 kcals/day. Supervised resistance training sessions will take place 2 days/wk and aerobic exercise will take place every day. During the resistance exercise sessions, subjects will engage in a circuit weightlifting routine using guided motion machines. During the aerobic sessions, subjects may choose whatever exercise modality they like (e.g. walking on track or treadmill, biking, elliptical, etc.). Subjects will wear devices that measure energy expenditure to get a better idea of the intensity and duration needed to expend 250 kcals with their exercise machine/modality of choice.

Behavioral: Dietary - Caloric Restriction

Subjects will be counselled on their respective hypocaloric diets during the 16 wk period. Adherence to the prescribed diet will be assessed via collection of assigned food records (biweekly), frequent contact with subjects, and regular dietary counseling sessions. The daily dietary energy deficit will be 500 kcal per day based on the subjects' estimated daily caloric requirements (based on height, weight, age, sex), multiplied by a sedentary activity factor.

Additionally, subjects will consume 2 drinks per day that will differ depending on their randomization allocation. Subjects in the Dairy Protein and High Dairy Protein group will be provided with dairy products (e.g. milk, cheese, yogurt) to consume on a weekly basis to help facilitate their prescribed dairy and dietary protein intake.

Experimental: High Dairy Protein

A group consuming twice daily drinks of 1% artificially sweetened chocolate milk (in 1.5 cup servings = 3 cups/d). Their diet contains 30% protein (as opposed to only 15% in the Con and DairyPro groups) with at least 50% of that coming from dairy sources.

Behavioral: Exercise - Aerobic and Resistance

Subjects will perform exercise (aerobic and resistance) 7d/wk and will exercise supervised 5d/wk. Exercise will be carried out to expend 250 kcals/day. Supervised resistance training sessions will take place 2 days/wk and aerobic exercise will take place every day. During the resistance exercise sessions, subjects will engage in a circuit weightlifting routine using guided motion machines. During the aerobic sessions, subjects may choose whatever exercise modality they like (e.g. walking on track or treadmill, biking, elliptical, etc.). Subjects will wear devices that measure energy expenditure to get a better idea of the intensity and duration needed to expend 250 kcals with their exercise machine/modality of choice.

Behavioral: Dietary - Caloric Restriction

Subjects will be counselled on their respective hypocaloric diets during the 16 wk period. Adherence to the prescribed diet will be assessed via collection of assigned food records (biweekly), frequent contact with subjects, and regular dietary counseling sessions. The daily dietary energy deficit will be 500 kcal per day based on the subjects' estimated daily caloric requirements (based on height, weight, age, sex), multiplied by a sedentary activity factor.

Additionally, subjects will consume 2 drinks per day that will differ depending on their randomization allocation. Subjects in the Dairy Protein and High Dairy Protein group will be provided with dairy products (e.g. milk, cheese, yogurt) to consume on a weekly basis to help facilitate their prescribed dairy and dietary protein intake.

Choosing to participate in a study is an important personal decision. Talk with your doctor and family members or friends about deciding to join a study.
To learn more about this study, you or your doctor may contact the study research staff using the Contacts provided below.
For general information, see Learn About Clinical Studies.

Please refer to this study by its ClinicalTrials.gov identifier: NCT00710398